The present invention relates to a circuit for electrical discharge machining, sometimes hereinafter refered to as "EDM". The circuit is designed for use with cavity sinker type EDM equipment in which an electrode is mounted on a ram and controlled in its up and down movements during cutting. There is necessarily provided a control for initiating the cycle time and another for controlling backup of the electrode and ram after the cutting is concluded. One of the basic elements of this invention is the provision of a rapid backup and approach servo feed circuit that operates to reduce down time between cutting cycles. A circuit and arrangement having a like purpose is shown and described in W. B. Shaffer U.S. Pat. No. 3,435,177 issued on Mar. 25, 1969 for "Servo Control Circuit for Electrical Discharge Machining Apparatus" which patent is of common ownership herewith.
In many cycle timer circuits, microswitches are used which determine the change of direction and speed of the electrode and the ram carrying it. This results in an unnecessarily complicated system and one subject to wear and to malfunction. The present circuit and system are controlled by a pair of independently operating timers so that the cycle timer is reliably controlled without any deviation or variation in its predictability.